This laboratory has shown that vitronectin (VN), undetectable in normal adult brain, is a major adhesive molecule in malignant astrocytomas in vivo, an is recognized by integrins alphavbeta3 and alphavbeta5. In addition, both integrins alphavbeta3 and alphavbeta5 mediate VN-directed migration of malignant astrocytoma cells. In an intracerebral acid mouse model of human malignant astrocytoma VN and integrin alphavbeta3 were shown to co-localize to the invading tumor margin in serial tissue sections, in contrast to integrin alphavbeta5 expression which was diffuse. This suggests a possible coordinated regulation of VN and integrin alphavbeta3 expression at the tumor margin. It is unclear whether VN and integrin alphavbeta3 are synthesized in an autocrine or paracrine manner in malignant astrocytoma and the role of integrin alphavbeta3 in malignant astrocytoma cell proliferation in vivo. This proposal will examine the hypothesis that a coordinated r upregulation of VN and integrin alphavbeta3 expression occurs in proliferating astrocytoma cells at the invading tumor margin, which promotes malignant astrocytoma cell proliferation in vivo. Specifically, this research will determine: 1) whether malignant astrocytoma cells expressing integrin alphavbeta3 are proliferating cells and whether malignant astrocytoma cells synthesize VN an integrin alphavbeta3 in an autocrine or paracrine manner in astrocytoma biopsies, utilizing double label immunohistochemistry with mouse mAb anti-beta3 and rabbit anti-proliferating nuclear antigen antibody, as well as in situ hybridization followed by immunohistochemistry with antisense VN riboprobe and mAb anti-beta3, respectively, and 2) the role of integrin alphavbeta3 in malignant astrocytoma cell proliferation in the intracerebral scid mouse model of human malignant astrocytoma, utilizing FACS selected beta3 positive and beta3 negative subclones of the wild type U-251MG cell line which expresses integrin alphavbeta3 on 30% of cells. Patients with malignant astrocytoma have a poor prognosis (nine month average survival), despite current chemo- and radiotherapeutic regimens. Completion of this work will allow construction of a detailed model of VN dependent astrocytoma cell invasion into the normal brain, specifically determining the role of integrin alphavbeta3. It will also produce data important in determining whether antagonists directed toward integrin alphavbeta3 would be necessary to inhibit astrocytoma cell proliferation and invasion in vivo. In addition, malignant astrocytoma is an ideal model in which to study VN-binding integrin function as VN is one of the few matrix proteins identified in these tumors, in contrast to most cancers; thus this is a relatively clean system in which to study VN-binding integrin function.